This invention is directed to flame retardant thermoplastic compositions comprising aromatic polycarbonate, their method of manufacture, and method of use thereof, and in particular impact-modified thermoplastic polycarbonate compositions having improved scratch resistance.
Polycarbonates are useful in the manufacture of articles and components for a wide range of applications, from automotive parts to electronic appliances. Because of their broad use, particularly in electronic applications, it is desirable to provide polycarbonates with scratch resistance and flame retardancy. Many known flame retardant agents used with polycarbonates contain bromine and/or chlorine. Brominated and/or chlorinated flame retardant agents are less desirable because impurities and/or by-products arising from these agents can corrode the equipment associated with manufacture and use of the polycarbonates. Brominated and/or chlorinated flame retardant agents are also increasingly subject to regulatory restriction.
Nonhalogenated flame retardants have been proposed for polycarbonates, including various fillers, phosphorus-containing compounds, and certain salts. It has been difficult to meet the strictest standards of flame retardancy using the foregoing flame retardants, however, without also using brominated and/or chlorinated flame retardants, particularly in thin samples.
Polysiloxane-polycarbonate copolymers have also been proposed for use as non-brominated and non-chlorinated flame retardants. For example, U.S. Application Publication No. 2003/0105226 to Cella discloses a polysiloxane-modified polycarbonate comprising polysiloxane units and polycarbonate units, wherein the polysiloxane segments comprise 1 to 20 polysiloxane units. Use of other polysiloxane-modified polycarbonates are described in U.S. Pat. No. 5,380,795 to Gosen, U.S. Pat. No. 4,756,701 to Kress et al., U.S. Pat. No. 5,488,086 to Umeda et al., and EP 0 692 522B1 to Nodera, et al., for example.
While the foregoing flame retardants are suitable for their intended purposes, there nonetheless remains a continuing desire in the industry for continued improvement in flame performance while also providing good scratch resistance and maintaining other mechanical properties such as ductility. Flame retardant impact modified polycarbonate blends have been used in a variety of applications such as computer and business equipment, battery chargers, industrial housings, and the like. There is a need for impact modified blends with high flow characteristics are an attractive choice to mold large housings such as flat panel TV bezels as they offer a combination of interesting properties, including the capability to fill long flow lengths, adequate mechanical strength and flame retardancy. These impact modified blends also need to be free of chlorine and bromine flame retardant agents, but non-brominated and/or non-chlorinated flame retardants can adversely affect desirable physical properties of the polycarbonate compositions, particularly impact strength. While many parts made from impact modified blends have good mechanical properties, parts made from these blends typically suffer from poor scratch resistance due to the presence of the impact modifier. There is a need for flame retardant blends that provide good scratch resistance in combination with good mechanical properties, such as ductility, and good flame performance.
Aromatic polycarbonates are useful in the manufacture of articles and components for a wide range of applications, from automotive parts to electronic appliances. Impact modifiers are commonly added to aromatic polycarbonates to improve the toughness of the compositions. The impact modifiers often have a relatively rigid thermoplastic phase and an elastomeric (rubbery) phase, and may be formed by bulk or emulsion polymerization. Polycarbonate compositions comprising acrylonitrile-butadiene-styrene (ABS) impact modifiers are described generally, for example, in U.S. Pat. No. 3,130,177. Polycarbonate compositions comprising emulsion polymerized ABS impact modifiers are described in particular in U.S. Publication No. 2003/0119986. U.S. Publication No. 2003/0092837 discloses use of a combination of a bulk polymerized ABS and an emulsion polymerized ABS.
Of course, a wide variety of other types of impact modifiers for use in polycarbonate compositions have also been described. While suitable for their intended purpose of improving toughness, many impact modifiers may also adversely affect other properties, such as processability, hydrolytic stability, flame performance, and/or low temperature impact strength, as well as scratch resistance. There remains a continuing need in the art, therefore, for impact-modified thermoplastic polycarbonate compositions having a combination of good physical properties, including impact strength, flow and flame performance as well as scratch resistance.